1. Field of the Invention
The present invention relates to a developer discharging device for an image forming apparatus, and more particularly, to developer discharging device for an image forming apparatus, which is capable of preventing a developer from being sharply discharged, and thus constantly maintaining an amount of the developer.
2. Discussion of Related Art
An image forming apparatus, such as a copy machine, a printer and a multifunction printer, is divided into an ink-jet type, an electro-photographic type and a thermal printing type. Here, in the electro-photographic type image forming apparatus, an image is formed on a print medium through a series of charging, exposing, developing, transferring and fixing processes.
A conventional electro-photographic type image forming apparatus includes a cartridge assembly in which a drum unit having a photoconductive drum, a charging roller and a transfer roller, and a developing unit configured to accommodate a developer therein and having a developing roller and a supplying roller are integrally formed.
Here, the cartridge assembly accommodates the developer including toner and carrier, and the developer should be refilled or replaced due to a consumption of the toner according to a printing operation.
In a conventional refilling/replacing method of the developer, a waste developer, i.e., a waste toner and a waste carrier were collected and discharged at the same time, and then a new developer was refilled. However, in the conventional method, an amount of the developer sent to a dump was large, and a separate waste developer receiving part was required.
An image forming apparatus which collects and reuses toner in consideration of a conventional developer consumption is disclosed in Japanese Patent Publication No. 1993-66659 (related document 1). The related document 1 discloses a process cartridge in which a waste toner tank is integrally installed at the photoconductive drum, and a discharging mechanism for collecting the waste toner of the waste toner tank into the developing machine is installed.
Also, an image forming apparatus which collects and reuses the toner and controls a carrier supply is disclosed in Japanese Patent Publication No. 2001-194908 (related document 2).
Here, in the conventional image forming apparatus including the above-described documents, a method of discharging the developer of the developing unit to the waste toner tank may be classified into a reverse pitch screw method and a dam method. In the reverse pitch screw method, all of the developers passing through a reverse pitch screw are discharged to the waste toner tank, and in the dam method, when an amount or a load of the developer arrives a predetermined level, the developer is discharged.
However, in the case of the reverse pitch screw method, since all of the developers passing through the reverse pitch screw are discharged, the developer may be sharply discharged due to an increase in an internal pressure of the developing unit or an overage of a new developer, and thus a change amount of the developer in the developing unit may be increased. This has a bad influence on print quality.
Also, in the case of the dam method, all of the developers over the predetermined level are discharged. Here, even when the amount of the developer is the same, a volume thereof is changed according to a ratio between the carrier and the toner. When a ratio of the toner is relatively great, an entire volume thereof is increased, and the level of the developer is increased. Therefore, the developer may overflow and then may be discharged, and thus the amount of the developer is reduced.